Electron beam furnaces are used to heat materials to produce vapors for deposition on an article. An electron beam furnace includes an electron gun, a deflection system, and a cooling system. The electron gun generates an electron beam. The deflection system directs the electron beam toward the material to be heated. The cooling system cools the electron gun to prevent it from overheating.
The electron gun typically includes an electron source, a focusing electrode, and an accelerating electrode. The electron source is typically a cathode heated by an electric current to cause the cathode to emit electrons. The focusing electrode is typically negatively charged to repel the electrons and thereby direct the electrons in a direction generally toward the accelerating electrode. The accelerating electrode is positioned downstream from the electron source and the focusing electrode. The accelerating electrode is typically less negatively charged than the electron source and the focusing electrode to cause the electrons to form into a beam and travel in the downstream direction.
In one known type of electron gun, the electron source and the focusing electrode are elongated and disposed in a head. The head is supported by a platform spaced apart from the accelerating electrode. This type of electron gun is reliable and available in many different power ratings. The physical size of the head, the accelerating electrode, and the platform of a given one of these electron guns depends on its power rating.
It is important that an electron gun to be used in an electron beam furnace generate an electron beam suitable for the type of material to be heated and the type of deposition sought for the article. Different types of materials and depositions require electron beams of different amounts of electron beam power and may require different electron beam shape. However, it is desirable to have electron beam guns operate in a space charge limited mode. In such mode, the above described type of electron guns generally perform best at a power equal to or slightly below its power rating. Consequently, no one of these electron guns can adequately generate electron beams for all of the electron beam powers required.
Whenever an electron gun in the electron beam furnace does not generate an electron beam suitable for the type of material to be heated and the type of deposition sought for the article, the traditional approach has been to remove the electron gun and replace it with an electron gun that provides a suitable electron beam. However completely replacing an electron gun can be difficult and time consuming. Moreover, the deflection system and the cooling system of the electron beam furnace are connected to the accelerating electrode of the electron gun and are designed to suit the physical size of the accelerating electrode and the power rating of the electron gun. Consequently, replacing the electron gun requires replacing the deflection system and the cooling system, thereby compounding effort involved.